Ireland Outcrops Still Yield Deep Secrets

Some come to view the dramatic, awe-inspiring beauty. They are not disappointed.

Others seek to decipher its vivid, detailed history of the earth, on full-display and to the trained eye, as readable as pages in a book.

But those looking for clues to new hydrocarbon discoveries are there with specific purpose – finding geological insight and understanding that will help bring exploration success around the world.

And they, most definitely, are finding what they seek.

The area is the Mississippian-Pennsylvanian deepwater-deltaic basin fill succession of western County Clare and northern County Kerry in western Ireland. This area exposes more than 2,000 meters (6,600 feet) of deepwater basin floor shales and sandstones, slope mudstones and sandstones and a thick deltaic succession deposited in a sedimentary basin (the Shannon/Clare basin) centered on the Shannon Estuary.

This area has been used by literally thousands of geoscientists from all over the world as a research and training area area since the 1950s, utilized by virtually all major petroleum companies for research and education courses, and has been the excursion site of an untold number of students – primarily from Europe, but also from North American universities.

And the value of the Clare Basin outcrops to explorationists has especially increased over the past two decades, as sandstone reservoirs within many deepwater basins and basin margins globally have been at the forefront of new exploration in the Gulf of Mexico, the South Atlantic basins such as Angola and Brazil, northwest European basins and in California.

“The value of outcrop analogs such as the Clare Basin for detailed understanding of exploration and production geological models cannot be underestimated,” said AAPG member Ole Martinsen, winner of the 2011 AAPG Robert R. Berg Outstanding Research Award.

“The stratigraphic context, spatial view of reservoir and seal rock character and dimensions lead to much better predictive models for exploration success,” he said, “and production effectiveness and efficiency.”

Many themes at the upcoming AAPG Annual Convention and Exhibition in Long Beach, Calif., will focus on deepwater reservoirs and their outcrop analogs – and Martinsen and his colleagues, citing their research and work on and at the rugged Irish coastal outcrops, will be presenting a lot of those papers.

“Some outcrop analogs that expose deepwater and related reservoirs have stood the test of time, over many decades, as global analogs for discovery of new insight, development of knowledge and not least as world-class training areas for literally thousands of geologists in the petroleum industry and academia,” he said.

Valuable Training Ground

The last decade saw a major resurgence of outcrop studies, facilitated by the advent of new technology such as LiDAR scanning, photorealistic mapping (see June 2004 EXPLORER), behind-the-outcrop drilling and remote sensing data.

“New outcrop technologies allow for refined interpretations, facilitated by more precise and higher-resolution, digital collection of data,” Martinsen said, “and also by allowing collection of data that compare with subsurface data.

“This increases the value of outcrop data enormously, and bridges between outcrops and the subsurface,” he said.

“In addition, seismic modeling allows for creation of synthetic seismic data that, combined with the digital and photorealistic outcrop data and the core and log data from the outcrop wells, allow for reservoir models to be created that compare directly with subsurface data,” he added.

A 2008 SEPM research conference organized by Martinsen, Peter Haughton (University College, Dublin, Ireland) and AAPG members Andrew Pulham and Morgan Sullivan in County Clare focused on the new outcrop technologies (published last year in SEPM’s “Concepts in Sedimentology and Paleontology”). These new technologies have been used in recent research phases by the authors in County Clare, and some of their new insights will be presented at the upcoming ACE.

Martinsen, Pulham, Haughton and AAPG member Trevor Elliott, a UK-based consultant and past AAPG Distinguisted lecturer, also are strongly involved in delivering training in the Clare Basin, and they all agree that the petroleum industry, universities and training companies “have long recognized the educational value of the Clare Basin.”

“Every year there are numerous field classes that use the exceptional coastal geology as primary training tools and as analogs for global application,” Pulham said.

“The outcrops are a particular favorite location for Irish students,” Haughton added, “not least from University College Dublin and Trinity College.”

“The popularity of the area has resulted in a very large community (thousands) within the AAPG membership that has visited and gained insights from the area,” Pulham said.

“A compelling draw is that many petroleum-rich margins around the world have reservoir rocks that are very comparable to those in the Clare Basin,” he continued, “(and) in tandem with the training opportunities, the outcrops have repeatedly delivered new insights to key geological concepts and methods, such as deepwater sedimentary processes and sequence stratigraphy.”

“Furthermore,” Haughton said, “the lessons for understanding reservoirs in the subsurface are continuing to be delivered – and currently this is via behind outcrop drilling in west Clare and north Kerry.”

The Borehole Project

In 2009, Statoil decided to sponsor a borehole project at the University College Dublin with Haughton and Pat Shannon as the principal investigators. The purpose has been to drill a series of behind-the-outcrop wells in the Ross Formation, a sandstone formation that bears very high resemblance to deepwater reservoirs in petroleum-rich basins around the world.

Including 2012 drilling there are 10 wells, covering different aspects of the formation – including classic, most-visited localities and new and inaccessible sections.

While the spectacular cliff sections show details of high importance, the well data are providing significant new results, such as stratigraphic insights and variability in sandstone bedding types, which previously have not been recognized in the dramatic cliff sections.

“Prior and recent studies on the stratigraphy have provided unsubstantiated results on both the biostratigraphy and on the correlation within the Ross Formation itself, and the cores in the wells show a bio-zonation that far surpasses previous understanding of the stratigraphy,” Martinsen said. “New understanding of deepwater sedimentary processes has developed, through the work of Peter Haughton and students on the core and log data.

“While classic turbidity currents forming turbidites until recently were thought to be the dominant sedimentary process in deepwater basins forming deepwater reservoirs, new insight from deepwater successions such as the core and log data from County Clare show very clearly that many sandstone beds are much more complex and deposited to a large degree by transitional flows carrying a large proportion of muds,” he said. “This impacts the quality of the reservoirs containing such beds, and currently many deepwater fields and reservoir units in petroleum-rich basins have this challenge.

“The Wilcox formation of the Gulf of Mexico basin is such an example,” he added, “but other basins, too, globally show the same challenge.”

Many companies holding acreage where this challenge is important have initiated outcrop work to understand the challenge better, according to Martinsen. Thus, well data with core and logs from the Clare Basin – combined with detailed outcrop work to see larger scale features – is essential to develop even better insight of the complexity of deepwater reservoirs, “at a time when many researchers have been comfortable with the classic and traditional understanding of these types of reservoirs.

“Having core and log data in basins like the Clare Basin, where the regional picture established, is thus very valuable for global implementation of these results,” Martinsen said.

Google It

Google Earth has played a big role in the most recent studies of Clare Basin.

Martinsen, Pulham, Haughton and Elliott, were by chance exploring the Clare coast using Google Earth for future research drilling locations ­– and were very pleasantly surprised to discover hitherto unknown value in an intertidal exposure of deepwater stratigraphy near Doonbeg in central Clare.

This overlooked and previously unstudied outcrop, exposed only at low tide, is a more than 200-meter thick succession that extends for over two kilometers along the coast – and it includes a seismic scale channel complex, possibly with levees.

“The reason this part of the coast has been neglected are the sweeping macro-tides and an assumed cover of recent sediments and seaweed in the area,” Martinsen said, “but in Google Earth the outcrop had been captured at ideal low tide, revealing the exquisite channel complex.

“This newly discovered geology adds significantly to the value of the slope succession in the Clare Basin as an analog for, for example, the Neogene succession in the Gulf of Mexico basin,” he added.

“The aerial images in Google Earth were key,” Martinsen said, “and again proves that new technology delivers new perspectives, insight and ideas.

“It is proven in geology that many new concepts, such as seismic and sequence stratigraphy (driven by 2-D seismic in the 1970s and 1980s), and the new detailed insight into deepwater sedimentary processes and reservoirs driven by 3-D seismic in the 1990s and 2000s,” he said.

“So is also the case for the wonderful and spectacular outcrops and global analogs seen in the Clare Basin,” he added. “New technology, delivered by the borehole project and by global satellite data, such as in Google Earth, delivers fabulous new insight not realized earlier.”

This story, according to the researchers, shows that it is important to hang in there:

“Geology in even classic, long-visited areas such as the Clare Basin goes through new phases of research and understanding,” Martinsen said, “but the big breaks come when new technology is applied.”

A Geologists’ Mecca

From the 1980s and still continuing, numerous petroleum companies have conducted research and training campaigns in the Clare Basin. Shell was one of the first to bring geologists from their global exploration and production projects to the area for training.

BP, Exxon, Chevron, Conoco, Norsk Hydro and Statoil also have invested heavily in the Clare outcrops.

Various academic institutions also have run their undergraduate and graduate field courses in the area – not least the Irish universities, but also major European and North American institutions.

Masters and doctoral research has resulted in a wealth of theses in the Clare Basin dating first from the 1950s and continuing today with two new graduate students at University College of Dublin and Trinity College. The latest research results will be presented by UCD doctoral candidate Colm Pierce at the upcoming ACE in Long Beach.

Interestingly, AAPG President Paul Weimer had a research student in the area in the early 2000s: David Pyles, who won the AAPG J.C. “Cam” Sproule Award in both 2009 and 2010 for his work.

In total, six decades of accumulated and continuing research and education have resulted in an unqualified estimate of the number of geoscientists visiting the Clare Basin at around 10,000 or more.

Ole Martinsen and his colleagues will make several technical presentations at the upcoming AAPG Annual Convention and Exhibition, set April 22-25 in Long Beach, Calif.

The presentation by Ole J. Martinsen focuses on the channel complex in the slope succession discovered in Google Earth, which adds significantly to how the deep-water sandstone succession in the Ross Formation is linked genetically to the shallow-water and deltaic sediments:

“Deepwater Slope Channels and Their Levees: New Insight From a Revisit to the Namurian (Early Pennsylvanian) Gull Island Formation, Western Ireland,” will be presented at 9:05 a.m. Monday, April 23.